The field of the invention generally relates to sonar fishfinder systems, and more particularly relates to apparatus and method for providing a visual A-Scope display of current returns or echoes from the transducer beam.
As is well known in the field of sonar, echo sounders, which are commonly referred to as depth sounders or fishfinders, are used to provide the user with a generalized picture or image of what is under a boat or other vessel. In particular, a transducer converts an electrical transmitter pulse into an ultrasonic or high frequency energy wave that is transmitted downwardly in the water. The energy or sound wave travels downwardly in a pattern substantially characteristic of a cone, and reflects upwardly from obstructions such as the sea bottom, fish, or other submerged objects. The returns or echoes are received by the transducer during a listening interval, and converted to electrical signals. A processor converts the electrical signals into an image which is displayed on a screen such as on a CRT or LCD display. As is well known, the elapsed time for pulse energy to travel down though the water and back up as an echo is measured by the processor, and used to determine the depth at which objects are displayed.
Commonly, fishfinders graphically display historical information of what has passed under the fishfinder's transducer as the boat moves along. Also, in what is commonly referred to as an A-scope display, a real time image of what is currently under the transducer is displayed, typically juxtaposed to the historical image. Further, it is common to provide a readout of a numerical value indicating the water depth, or depth to the sea bottom. However, one drawback expressed by users is that it may be difficult to determine how far the fish are laterally from the side of the boat. For example, in the A-scope display, the user may know that fish are in the cone of the transducer beam near the bottom, and that the depth is, for example, 100 feet. However, he doesn't know how far laterally or horizontally the fish could be. Therefore, he doesn't know whether to keep his line close to the side of the boat, or also to try casting away from the boat.